Analyzing reconstruction scenarios for dolmen D14 using non-destructive, digital methods
With a focus on the dislocated capstone
E.L. Theuws (TU Delft - Civil Engineering & Geosciences)
D.J.M. Ngan-Tillard – Mentor (TU Delft - Geo-engineering)
Linh Truong Truong-Hong – Graduation committee member (TU Delft - Optical and Laser Remote Sensing)
A.A. Mehrotra – Graduation committee member (TU Delft - Applied Mechanics)
RC Lindenbergh – Graduation committee member (TU Delft - Optical and Laser Remote Sensing)
G. Giardina – Graduation committee member (TU Delft - Geo-engineering)
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Abstract
The lack of insight regarding the stability of many dolmen in the Netherlands is problematic. In 2019, a capstone fell down dolmen D14, greatly damaging this cultural heritage. In order to decide on whether it would be wise to reconstruct this dolmen, it is useful to understand the stability of potential reconstruction scenarios without having to perform invasive tests that could damage the structure. To this end, this research has focused on the application of non-destructive, digital methods to analyze the stability of dolmen D14. Laser scanners were used to obtain point cloud data from the zone around the dislocated capstone, with which 3D meshes were created. Furthermore, tests were conducted to estimate the relevant parameters to quantify the shear strength of the rock contact areas. This was done in the field using the Equotip and Barton’s comb and by performing tilt tests and Golder shear box tests in the laboratory. For the rock parameters, a basic friction angle of 33° was found with tilt tests and a residual friction angle of 31.2° and 30.5° was found for the Golder shear box on a flat sample. The meshes and rock parameters were used as input to conduct stability analyses in 3DEC. Two different models were analyzed, one based on the rock configuration as it was in 2019 (Model 1) and the second model with a rock configuration as it was in 1925 (Model 2). In the stability analysis, it was found that Model 1 is much more unstable compared to Model 2. The minimum pushing force for instability of the structure was 2 kN for Model 1 and 94 kN for Model 2, for the conditions under research. Furthermore, it was found that the number of cycles used in the analysis, mesh coarseness and rock joint friction angle all have a significant impact on the model results. All in all, this research has demonstrated the potential for using digital and non-destructive methods to analyze the stability of megalithic structures.